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Using cleaner fuels, such as hydrogen and developing more efficient combustion technologies are crucial in reducing NO x and N 2 O emissions, contributing to environmental concerns like air pollution and global warming. However, studies focusing on gas turbines using H 2 as fuel often overlook the emissions resulting from H 2 combustion. Given that gas turbines play a significant role in electricity generation globally, even minor improvements in their efficiency can lead to substantial cumulative benefits. Therefore, this study aims to address this gap by conducting a comprehensive environmental assessment using the life cycle assessment (LCA) methodology. By evaluating the environmental impacts of emissions from the combustion process of a conventional gas turbine and comparing them with potential emissions from H 2 combustion, this research seeks to provide valuable insights into the overall environmental performance of these technologies and contribute to sustainable energy development efforts. There have already been several LCA studies on H 2 production. In this study, we have identified the potential emissions and environmental impacts of H 2 combustion in gas turbines and compared them with the impact values of H 2 production regarding reference studies. The result shows that emissions during combustion should be considered in the identified life cycle impact categories. • Emissions released during hydrogen combustion are analyzed by gate to gate LCA. • AP values were found to be more sensitive to increasing NOx emission than EP and ODP. • GWP values due to N 2 O emission were determined as 0.72–1.11 E−4 kg CO 2 -eq. • Sensitivity analysis indicates that higher turbine efficiency reduces GWP. • This work highlights that emissions released during combustion are considerable. [ABSTRACT FROM AUTHOR]

Small hydro technology is playing a crucial role in advancing sustainable, clean energy policies as part of the global hydro development strategy. Its contribution to social and economic development is becoming more prominent, particularly in ensuring electricity access for rural communities and supporting industrial expansion. The main causes of bulb turbine failures under high operating conditions are frequently attributed to variations in pressure in the draft tubes, which are aggravated when a spinning vortex rope is formed under load operation. Different fluid injection techniques, namely compressed air and water jet injection, address these issues and reduce the negative results of cavitation. The investigation covers the flow visualization on the suction side of a single hydrofoil utilizing a cavitation tunnel and a bulb turbine. This study assesses the effectiveness of compressed air injection in reducing vibration generated by cavitation in bulb turbines. Positive results of the experimental studies suggest a decrease in noise and vibration by air injection that prevents oscillations of the vortex rope. This research also considers how the hydrofoil design of bulb runner blades influences flow characteristics. Hence, it provides knowledge on cavitation structures in diverse cavitation numbers. Different studies that compare the original and modified hydrofoil designs reveal remarkable improvements that may be due to changes in the key parameters of the hydrofoil, such as later cavitation initiation and reduced intensity. To obtain the optimal output of a bulb turbine by considering air injection for vibration reduction and hydrofoil design changes to limit the negative effect of cavitation, the Reynolds number and cavitation number are to be defined. This multidisciplinary approach possesses enormous potential to increase the reliability and efficiency of bulb turbines in challenging operating conditions. [ABSTRACT FROM AUTHOR]

Purpose: Life cycle assessment (LCA) distinguishes three types of water use: (1) consumptive water use, (2) degradative water use, and (3) in-stream water use. When it comes to assessing the impact of turbine water use (TWU, major source of in-stream water use) in LCA, so far, no method exists to quantify the related environmental impacts. Here, we developed the first midpoint characterization factors (CFs) with global coverage for turbine water use of storage and pumped storage hydropower power plants. Methods: The midpoint CF at the basin scale describes the hydropower regulation potential (HRP) [HDOR·y] per TWU [m3]. The HRP indicates the probability of how strongly the natural flow regime of a river is potentially affected by all upstream reservoir operation, calculated as the quotient between reservoir volume [m3] and the annual river discharge [m3/y]. The hydropower degree of regulation (HDOR) thereby equals the unitless m3/m3 fraction. The TWU depends on the electricity production [kWh] and the turbine efficiency [m3/kWh]. We tested the sensitivity of the input data on the calculated CFs for four parameters (discharge, turbine efficiency, multipurpose allocation, and plant type). Furthermore, we performed a case study to analyze if consumptive and TWU impacts of producing 1 kWh are correlated or not. Results and discussion: The calculated CFs for the 342 basins vary from 1.13E-13 HDOR·y/m3 to 3.28E10-7 HDOR·y/m3. The HDOR values range from 0.0015 to 16.66, and the TWU varies between 0.0030 km3 and 2824 km3. A HDOR ≥ 0.02 can be interpreted as affected basin, and only 23 out of 342 basins have a HDOR below this threshold. This confirms that TWU of hydropower production can have important environmental impacts. The sensitivity analyses revealed that discharge and turbine efficiency are the most sensitive parameters because they are influencing almost all basins. The results of the case study showed that a high consumptive water-use impact does not automatically lead to a high TWU impact and vice versa (R2 values of 0.0081 and 0.003). Conclusion: Our study highlights that it is important to account for the environmental impacts of in-stream water use in LCA, as otherwise, the environmental impact can be underestimated, which could lead to wrong conclusions. However, the CFs are not meant to replace a local risk assessment of hydropower reservoir operation and should only be used for relative comparison between basins. The CF application in LCA will represent a step forward towards more sustainable hydropower development. [ABSTRACT FROM AUTHOR]

Higher thermal efficiency of gas turbines needs higher turbine inlet temperature, which is a challenge for temperature tolerance of turbine blades. Therefore, it is vital to propose and investigate advanced internal cooling structures. In this study, a Double-paths V ribbed U channel for rotating blade cooling is proposed and researched through heat transfer experiments of transient liquid crystal and flow simulations of Reynolds-averaging Navier–Stokes approaches in the conditions of Reynolds number (Re) at 16 000 and Rotation number (Ro) at 0, 0.006, and 0.024. The definition of the Double-paths V ribbed U channel is that it is a rotating U channel arranged from blade pressure side to suction side and that there are double passages from the pressure side to suction side from the cross section view of the blade. The novelties of the study are to reveal the interactions of V rib-induced, bend-induced, and Coriolis force-induced vortices and to unveil the heat transfer distributions and enhancement mechanisms with various Ro. Besides, the thermal and flow characteristics between the Double-paths V ribbed U channel and Double-paths 45° ribbed U channel are comparatively investigated as well. The results manifest that with identical pumping power, the Double-paths V ribbed U channel can achieve ascending heat transfer improvement as Ro rises owing to exploiting the positive heat transfer influence of Coriolis force on the pressure and suction sides, indicating that the channel is an inspiring and promising rotating structure applied for rotor blade internal cooling. [ABSTRACT FROM AUTHOR]

There is a growing demand to improve the performance of vertical axis wind turbines to facilitate their commercialization for application in urban areas. This study utilizes a 3D numerical analysis to examine the influence of different vortices generated on turbine efficiency with straight and J‐type blades. The numerical simulation of this study employs the Reynolds‐Averaged Navier–Stokes equations and ‎sliding ‎mesh techniques ‎to more accurately model the rotational motion of blades about the turbine axis in relation to the ‎wind. Comparing the output ‎torque and the flow field at different span‐wise sections, the J‐type blades achieve better ‎performance at mid‐spans where the effect of stall vortices is dominant. Conversely, the lower ‎performance of J‐type blades is seen at tip spans due to stronger tip vortices. Investigations also ‎reveal the criticality of the downwind region on the overall performance at high tip speed ratios. It is observed that by ‎increasing the height, the tip vortices are limited to the tip sections, and stall vortices expand further ‎along the blade. At TSR = 1, the improvement by J‐type blades rises from 10% at a height of 0.8 m to 44% ‎at 3 m. The growth in height at lower wind speeds becomes more beneficial. Compared to the straight blades, the self‐starting ‎generated torque by J‐type blades for heights of 0.8, 1.2, and 1.6 m, are improved by 15.6%, ‎‎26.9%, and 34.7%, respectively. Overall, it is concluded that by increasing the blade height, the superiority ‎of the J‐type blade becomes more noticeable as the blade mainly contributes to suppressing the stall ‎vortices effect where the tip vortices effect is not presented. ‎ [ABSTRACT FROM AUTHOR]

This study investigates the flow dynamics and energy losses of Tesla turbines using Computational Fluid Dynamics with OpenFOAM. Our goal is to identify the main sources of energy loss. Four main sources of energy loss were identified. The most significant loss occurred during the conversion of pressure energy to kinetic energy, estimated to range from 88% to 64% of the total energy. Energy losses due to leaks between the rotor and the casing were also quantified, ranging from 4.97% to 7.95% of the kinetic energy at peak efficiency points. Design modifications, such as incorporating a nozzle at the entrance of the turbine, can improve efficiency. These findings highlight specific areas for efficiency improvement, offering opportunities for improved turbine design and integration into energy‐generation systems. [ABSTRACT FROM AUTHOR]

By utilizing the similarity characteristics of turbines, their performance can be tested under conditions more relaxed than the design conditions. The use of the similarity model provides the benefit of saving time and the cost required to build a turbine test bench for the performance measurements. This study employs a partial similarity model, rather than a complete similarity model, with a rotational speed of 6000 rpm and air as the working fluid. Condition selection for this model was based on Buckingham's Pi theorem to nondimensionalize the parameters affecting turbine performance. Particularly, the pressure ratio was derived using in-house code. Based on mean-line design results, three-dimensional modeling and numerical analysis were performed using commercial software to compare the performances of the design and partial similarity models. The numerical analysis predicted the isentropic efficiencies of 86.1 % and 80.4 % for the design and partial similarity models, respectively. This study is significant as it enables turbine performance testing at a lower rotational speed with air as the working fluid. [ABSTRACT FROM AUTHOR]

The generation of sustainable energy through wind and hydrokinetic turbines, which convert the kinetic energy from fluid flows into mechanical energy, presents an attractive solution for diversifying the country energy matrix in response to climate change. Consequently, numerous studies have investigated the aerodynamic and hydrodynamic behaviors of various wind and hydrokinetic turbines using numerical simulations to understand their interaction with the surrounding fluid flows and enhance their performance. However, to validate these studies and aiming at improving the turbine design, experimental studies on a laboratory scale employing wind tunnels and hydraulic channels are essential. This work addresses the development and implementation of a reliable control system for experimentally evaluating the power coefficient (Cp) versus the tip speed ratio (TSR) curve of wind and hydrokinetic turbines. The control system, based on a DC motor acting as a generator and aligned with a commercial torque sensor, enables a precise control over the experimental setup. By obtaining and comparing the experimental performance curves of Cp versus TSR for both wind and hydrokinetic turbines with numerical results, the effectiveness and accuracy of the developed control system are demonstrated. A satisfactory fit between numerical and experimental results was achieved, underscoring the utility and reliability of the control system for assessing the turbine performance. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study on the impact of erosion on the flow characteristics through the blade of the last stage of a 900 MW steam turbine. The primary objective is to understand how surface erosion, caused by prolonged steam exposure, affects flow behavior and the overall efficiency of a 900 MW class turbine. The research process began with a 3D scan of the turbine blade, using advanced laser scanning technology to create a detailed geometric model. As one of the longest blades used in steam turbines, it posed both a technical challenge and was an innovative aspect of this study. The resulting 3D model served as the basis for numerical simulations using Computational Fluid Dynamic (CFD) methods, which allowed for the analysis of steam flow over the eroded blade surface. Key flow parameters, including velocity, pressure, and turbulence, were assessed to determine the impact of erosion. The study revealed significant changes in flow characteristics depending on the degree of erosion, providing valuable insights for turbine optimization and maintenance. The novelty of this research lies not only in the use of advanced scanning technologies but also in analyzing one of the longest blades in industrial practice, with findings that could enhance turbine efficiency and inform new erosion risk management strategies. [ABSTRACT FROM AUTHOR]

Under partial load operating conditions, vortex rope generation in the draft tube of a Francis turbine is considered one of the main reasons for hydro unit vibration. In this paper, a Francis turbine HLA551-LJ-43 in the laboratory was taken as a prototype. Numerical simulations of the entire flow passage were carried out. Four different hydro-turbines were chosen to analyze the effect of vortex suppression, which were named the prototype turbine (N-J), the turbine with J-grooves installed on its conical section (W-J), the one with extending runner cone (C), and the one that considered the J-grooves and the extending runner cone at the same time (J+C). Under the part load conditions in which the vortex rope is easily generated (0.4–0.8 times design flow QBEP), the spectrum characteristics of pressure fluctuation, the morphology of vortex rope, and the energy dissipation based on the entropy production theory in the draft tube were studied. The results show that the three optimized structures W-J, C, and J+C could reduce the pressure pulsation in the conical section of the draft tube, weaken the eccentricity of the vortex rope, and decrease the energy losses in the runner and draft tube. It is worth mentioning that the turbine with a J+C optimized structure had the most potent effect on vortex suppression and energy dissipation. Primarily when operating in deep partial load (DPL) conditions, the efficiency of the turbine with a J+C optimized structure was increased by 13.7% compared to the prototype turbine, and the main frequency amplitude of the pressure pulsation in the draft tube was reduced to 32% of the prototype. [ABSTRACT FROM AUTHOR]

The demand for clean and sustainable energy has led to the exploration of innovative technologies for renewable energy generation. The Savonius turbine has emerged as a promising solution for harnessing wind energy in urban environments due to its unique design, simplicity, structural stability, and ability to capture wind energy from any direction. However, the efficiency of Savonius turbines poses a challenge that affects their overall performance. Extensive research efforts have been dedicated to enhancing their efficiency and optimizing their performance in urban settings. For instance, an axisymmetric omnidirectional deflector (AOD) was introduced to improve performance in all wind directions. Despite these advancements, the effect of wind incident angles on Savonius turbine performance has not been thoroughly investigated. This study aims to fill this knowledge gap by examining the performance of standard Savonius configurations (STD) compared to the basic configuration of the deflector (AOD1) and to the optimized one (AOD2) under different wind incident angles and wind speeds. One key finding was the consistent superior performance of this AOD2 configuration across all incident angles and wind speeds. It consistently outperformed the other configurations, demonstrating its potential as an optimized configuration for wind turbine applications. For instance, at an incident angle of 0°, the power coefficient of the configuration of AOD2 was 61% more than the STD configuration. This ratio rose to 88% at an incident angle of 20° and 125% at an incident angle of 40°. [ABSTRACT FROM AUTHOR]

Water energy is one of the potential renewable energy, the problem so far has a low efficiency of the blade Pelton shape. So it takes a series of tools to know characteristics and performance of the Pelton turbine as a hydroelectric power plant in this research. Pelton turbines work by utilizing the potential energy of water stored at a certain head, which flows through a penstock/pipe that is equipped with a nozzle at the end. The high head causes the water to be under high pressure when it reaches the nozzle. The water coming out of the nozzle becomes kinetic energy in the form of a pressurized water jet, which is used to rotate the runner of the Pelton turbine. In this study, the effect of the number of nozzles used to rotate the Pelton turbine was analyzed, with the result that the number of nozzles is directly proportional to the efficiency of the Pelton turbine. Where the highest efficiency value is obtained by using 3 nozzles with a maximum efficiency value of 13.7 %, at 2 nozzles of 12.209 % and at 1 nozzle of 8.82 %. [ABSTRACT FROM AUTHOR]

This study investigates the influence of topography on wind turbine flow and power efficiency. Specifically, a standalone wind turbine is positioned at the top of idealized two-dimensional hills, and the effects of hill geometry and turbine position are systematically investigated. Various parameters are studied, including hill slope, distance between the leeward side of the hill and the turbine, turbine hub height, and hill size. Overall, it is observed that the turbine wake is consistently stronger in the hill cases compared to the flat case. This is attributed to two characteristics of hill flows: (1) the negative streamwise velocity gradients on the leeward side of the hills and (2) the reduced turbulence above the hilltops and hill wake regions. In addition, it is observed that the turbine induction factor is consistently increased in the hill cases compared to the flat case, while the turbine power and thrust coefficients are reduced. In practice, this means that turbines on the hills produce less power output than those on flat terrain for an equivalent wind potential, with the potential decrease in power output reaching more than 20 % for certain cases. Altogether, the results offer new insights into the effect of topography on turbine power efficiency. In addition, the study identifies clear relationships between the turbine power coefficient, the induction factor, the overall maximum deficit, and the base flow pressure gradient. These relationships could potentially be used to predict the change in power efficiency based on the wake flow or the base flow. Overall, the results show a clear connection between the turbine power efficiency and the turbine wake development. [ABSTRACT FROM AUTHOR]

Twin-web turbine discs have been the subject of research recently in an effort to lighten weight and boost aeroengine efficiency. In the past, the cooling design of turbine discs was generally constrained to optimizing a single structural parameter, which hindered the enhancement of the optimization impact. Therefore, this article proposes a twin-web turbine disc system with a high radius pre-swirl. Driven by the database produced through the numerical simulation, a backpropagation network surrogate model is constructed, and the angles of the pre-swirl nozzles and receiver holes are optimized by a genetic algorithm to enhance the cooling efficiency of the turbine disc. Evaluation was based on the highest disc temperature, disc temperature uniformity, and Nusselt number. The results demonstrate that the suggested surrogate model effectively optimizes the structural characteristics of the twin-web turbine disc by aiming for the specified cooling performance indexes. The cooling effect of the turbine disc is significantly improved in different operating environments. Specifically, the optimized model produces the largest temperature drop in the disc rim temperature. Both axial and radial temperature uniformity have led to a notable enhancement. The alteration in coolant flow within the cavity results in a notable decrease in the area with low heat transfer efficiency and a substantial increase in the Nusselt number. [ABSTRACT FROM AUTHOR]

With the progress of research on ocean thermal energy conversion, the stabI have checked and revised all. le operation of ocean thermal energy conversion experiments has become a problem that cannot be ignored. The control foundation for stable operation is the accurate prediction of operational performance. In order to achieve accurate prediction and optimization of the performance of the ocean thermal energy conversion experimental platform, this article analyzes the experimental parameters of the turbine based on the basic experimental data obtained from the 50 kW OTEC experimental platform. Through the selection and training of experimental data, a GA-BP-OTE (GBO) model that can automatically select the number of hidden layer nodes was established using seven input parameters. Bayesian optimization was used to complete the optimization of hyperparameters, greatly reducing the training time of the surrogate model. Analyzing the prediction results of the GBO model, it is concluded that the GBO model has better prediction accuracy and has a very low prediction error in the prediction of small temperature changes in ocean thermal energy, proving the progressiveness of the model proposed in this article. The dual-objective optimization problem of turbine grid-connected power and isentropic efficiency is solved. The results show that the change in isentropic efficiency of the permeable device is affected by the combined influence of the seven parameters selected in this study, with the mass flow rate of the working fluid having the greatest impact. The MAPE of the GBO model turbine grid-connected power is 0.24547%, the MAPE of the turbine isentropic efficiency is 0.04%, and the MAPE of the turbine speed is 0.33%. The Pareto-optimal solution for the turbine grid-connected power is 40.1792 kW, with an isentropic efficiency of 0.837439. [ABSTRACT FROM AUTHOR]

For floating wind turbines, one of the most interesting and challenging issues is that the movement of the rotor is strongly related to its floating platform, which results in corresponding variations in the wake characteristics of the turbine. Because the aerodynamic efficiency of the downstream turbines is affected by the wake characteristics, the power output will consequently vary depending on the different types of floating wind turbines and floating wind farms used. In this study, the rotor movement, wake characteristics, and corresponding wind farm power output are analyzed using a numerical method for three typical floating wind turbines: the semisubmersible type, spar buoy type, and tension leg platform type with a 5 MW configuration. A fixed-bottom monopile wind turbine is adopted as a benchmark. The simulation results show that of the three floating wind turbines, the rotor position and wake center are most dispersed in the case of the spar buoy type, and its wake also has the lowest impact on downstream wind turbines. Additionally, the power output of the corresponding spar buoy type wind farm is also the highest at different wind speeds, followed by the semisubmersible type, tension leg platform type, and then the fixed-bottom type. In particular, at low wind speeds, the wake effects differ significantly among the various types of wind turbines. [ABSTRACT FROM AUTHOR]

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study provides a numerical investigation about J‐shaped straight‐bladed Darrieus vertical axis wind turbines equipped with outboard, inboard, and two‐sided Gurney flap (GF). The performance of the turbines is examined for different GF heights and tip speed ratios (TSRs). The aerodynamic analysis is carried out using power curves, vorticity field, and pressure field surrounding the wind turbine. The results indicate that employing the inboard GF effectively enhances the turbine's performance by harnessing the drag force in the desired direction and postponing the flow separation up to 14° of azimuth angle. The inboard GF with a height of 0.75% chord length exhibits the best performance among the GFs, showing an increase in output power at higher TSRs up to 12.35%. Conversely, the use of outboard and two‐sided GFs of any height cannot improve the turbine efficiency. [ABSTRACT FROM AUTHOR]

Based on economic feasibility, renewable generators can use pumped hydro storage (PHS) to improve their profitability by performing energy arbitrage under real-time pricing (RTP) schemes. In this paper, we present a new method to optimise the size of and manage utility-scale wind–PV systems using PHS with energy arbitrage under RTP. PHS is used to supply load consumption and/or energy arbitrage. Further, both load-supply and power-generating systems are considered, and a genetic algorithm metaheuristic technique is used to perform the optimisation efficiently. Irradiance, wind speed, temperature, hourly electricity price, component characteristics, and financial data are used as data, and the system is simulated in 15 min time steps during the system lifetime for each combination of components and control variables. Uncertainty is considered for the meteorological data and electricity prices. The pump and turbine efficiencies and available head and penstock losses are considered as variables (not fixed values) to obtain accurate simulations. A sample application in Spain is demonstrated by performing a sensitivity analysis of different locations, electricity prices, and costs. PHS is not worth considering with the present cost of components. In load-supply systems in Zaragoza (Spain), we found that PHS would be worth considering if its cost was lower than 850 EUR/kW (considering all PHS components except reservoirs) +20 EUR/m3 for reservoirs (equivalent to 105 EUR/kWh with a 70 m head), whereas in Gran Canaria Island (with a considerably higher irradiation and wind speed), the required PHS cost is considerably lower (~350 EUR/kW + 10 EUR/m3). For power-generating systems, PHS required costs ranging from 400–700 EUR/kW + 15–20 EUR/m3 for obtaining the optimal PV–wind–PHS system with economic results similar to those of the optimal power-generating system without PHS. Thus, the renewable–PHS system with energy arbitrage under RTP could be profitable for many locations globally given the wide range of the PHS cost; however, each case is different and must be evaluated individually. The presented model can be used for optimising the renewable–PHS system in any location with any costs and RTP schemes. [ABSTRACT FROM AUTHOR]

In this study, a vertical-axis helical-blade water turbine is innovatively proposed by drawing on the design scheme of the traditional straight-blade turbine, compared to which this blade form can effectively improve the self-starting capability and energy capture efficiency of the turbine. The study analyzes the hydrodynamic performance of the device under different parameters using CFD (computational fluid dynamics) software STAR-CCM+ and overlapping mesh technique, and the CFD simulation results are verified with published experimental work. First, the design concept of the hydraulic turbine is presented, focusing on the design of the blades and transmission mechanism to ensure the stability of the structure. Second, the effect of two-dimensional parameters on the flow field characteristics and efficiency is investigated, and then three-dimensional design parameters, such as blade helix angle and hub-to-tip ratio, are considered. The results show that a 20% increase in blade density results in a 10.74% increase in efficiency. Regarding flow velocity, a maximum output of 2.4 kW was achieved for four operating conditions (1.0, 1.5, 2.0, and 2.5 m/s). In addition, the average dynamic torque of the helical-blade turbine was 16.44% higher than that of the straight-blade turbine, indicating superior self-starting capability. It was also found that at an aspect ratio of 1.5–1.75 and a helix angle of 80°, the energy capture efficiency of the helical-blade turbine was 33.7%, which was 45.3% higher than that of the straight-blade turbine. Comparative analysis shows that the vertical-axis helical-blade turbine has favorable hydrodynamic performance, especially under low flow conditions, and the design scheme shows obvious advantages, which makes up for the defects of the traditional vertical-axis straight-blade turbine with poor self-starting ability and low efficiency, and fills up the research gaps of vertical-axis turbine design optimization, which is of certain research value. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai Jiao Tong University (1006-2467) is the property of Journal of Shanghai Jiao Tong University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Identifying and analyzing the engine performance and emission characteristics under the condition of performance decay is of significant reference value for fault diagnosis, condition-based maintenance, and health status monitoring. However, there is a lack of relevant research on the currently popular marine large two-stroke dual fuel (DF) engines. To fill the research gap, a detailed zero-/one-dimensional (0D/1D) model of a marine two-stroke DF engine employing the low-pressure gas concept is first established in GT-Power (Version 2020) and validated by comparing the simulation and measured results. Then, three typical types of turbocharger performance decays are defined including turbine efficiency decay, turbine nozzle ring area decay, and turbocharger shaft mechanical efficiency decay. Finally, the three types of decays are introduced to the engine simulation model and parametric runs are performed in both diesel and gas modes to identify and analyze their impacts on the performance and emission characteristics of the investigated marine DF engine. The results reveal that turbocharger performance decay has a significant impact on engine performance parameters, such as brake efficiency, engine speed, boost pressure, etc., as well as CO2 and NOx emissions, and the specified limit value on certain engine operational parameters will be exceeded when turbocharger performance decays to a certain extent. The changing trend of engine performance and emission parameters as turbocharger performance deteriorates are generally consistent in both operating modes but with significant differences in the extent and magnitude, mainly due to the distinct combustion process (Diesel cycle versus Otto cycle). Furthermore, considering the relative decline in brake efficiency, engine speed drop, and relative increase in CO2 emission, the investigated engine is less sensitive to the turbocharger performance decay in gas mode. The simulation results also imply that employing a variable geometry turbine (VGT) is capable of improving the brake efficiency of the investigated marine DF engine. [ABSTRACT FROM AUTHOR]

Wave energy converters (WECs) utilizing the Oscillating Water Column (OWC) principle have gained prominence for harnessing kinetic energy from ocean waves. This study explores an innovative approach by transforming the pivoting Denniss–Auld turbine blades into a fixed configuration, offering a simplified alternative. The fixed-blade design emulates the maximum pivot points during the OWC's exhalation and inhalation phases. Traditional Denniss–Auld turbines rely on complex hub systems to enable controllable blade rotation for performance optimization. This research examines the turbine's efficiency without mechanical actuation. The simulations were conducted using ANSYS™ CFX 2023 R2 to solve the three-dimensional, incompressible, steady-state Reynolds-Averaged Navier–Stokes (RANS) equations, employing the k-ω SST turbulence model to close the system of equations. A grid convergence study was performed, and the numerical results were validated against available experimental and numerical data. An in-depth analysis of the intricate flow field around the turbine blades was also conducted. The modified Denniss–Auld turbine demonstrated a broad operating range, avoiding stalling at high flow coefficients and exhibiting performance characteristics like an impulse turbine. However, the peak efficiency was 12%, significantly lower than that of conventional Denniss–Auld and impulse turbines. Future research should focus on expanding the design space through parametric studies to enhance turbine efficiency and power output. [ABSTRACT FROM AUTHOR]

As an advanced energy storage technology, the compressed CO2 energy storage system (CCES) has been widely studied for its advantages of high efficiency and low investment cost. However, the current literature has been mainly focused on the TC-CCES and SC-CCES, which operate in high-pressure conditions, increasing investment costs and bringing operation risks. Meanwhile, some studies based on the phase-change CO2 energy storage system also have had the disadvantages of low efficiency and the extra necessity of heat or cooling sources. To overcome the above problems, this paper proposes an innovative compressed CO2 phase-change energy storage system. During the energy charge process, molten salt and water are used to store heat with a smaller temperature difference in heat exchangers, and high-pressure CO2 is reserved in liquid form. During the energy discharge process, throttle expansion is applied to realize the evaporation at room temperature, and CO2 absorbs the reserved heat to improve the power capacity in the turbine and the system energy storage efficiency. The thermodynamic and exergoeconomic studies are performed firstly by using MATLAB. Then, the parametric study based on energy storage efficiency, system unit product cost, and exergy destruction is analyzed. The results show that energy storage efficiency can be improved by lifting liquid CO2 pressure as well as compressor and turbine isentropic efficiencies, and CO2 evaporation pressure has the optimal pressure point. The system unit product cost can be reduced by decreasing liquid CO2 pressure and compressor isentropic efficiency, while CO2 evaporation pressure and turbine isentropic efficiency both have optimal points. Finally, the optimization of two performances is performed by NSGA-II, and they can reach 75.30% and 41.17 $/GJ, respectively. Moreover, the optimal energy storage efficiency is obviously higher than that of other energy storage technologies, indicating the great advantage of the proposed system. This study provides an innovative research method for a new type of large-scale energy storage system. [ABSTRACT FROM AUTHOR]

This article introduces a novel model reconstruction method for machining turbine blades damaged in service and repaired via additive manufacturing (AM). Addressing the lack of a model for damaged parts crucial for precise adaptive machining, the method involves model registration and construction. Initially, the AM-repaired blade is aligned with a theoretical CAD model through rough registration using Principal Component Analysis (PCA), followed by precise alignment within the blade profile's tolerance zone. The model construction employs the minimum curve energy principle to ensure seamless integration with undamaged areas and adherence to profile tolerance constraints. The interfacial profile curve between the undamaged and AM-repaired areas is used as the original curve to construct the curves in the AM-repaired area. The reconstructed curves are modified with a double constraint of being smooth and minimum occupation of the theoretical model tolerance zone. The efficacy of this method is validated through a case study. The repaired blade showed deviations from −0.101 mm to 0.115 mm, within profile tolerances, and a surface smoothness difference of less than 6.41 μm between the damaged and undamaged sections. This method significantly improves the precision and efficiency of turbine blade repair, offering substantial benefits for the turbomachinery manufacturing industry. [ABSTRACT FROM AUTHOR]

Heat exchangers make it possible to utilize energy efficiently, reducing the cost of energy production or consumption. For example, they can be used to improve the efficiency of gas turbines. Improving the efficiency of a heat exchanger directly affects the efficiency of the device for which it is used. One of the most effective ways to intensify heat exchange in a heat exchanger without a significant increase in mass-dimensional characteristics and changes in the input parameters of the flows is the introduction of turbulators into the heat exchangers. This article investigates the increase in efficiency of heat exchanger apparatuses by introducing turbulent lattice structures manufactured with the use of additive technologies into their design. The study is carried out by numerical modeling of the heat transfer process for two sections of the heat exchanger: with and without the lattice structure inside. It was found that lattice structures intensify the heat exchange by creating vortex flow structures, as well as by increasing the heat exchange area. Thus, the ratio of convection in thermal conductivity increases to 3.03 times. Also in the article, a comparative analysis of the results obtained with the results of heat transfer intensification using classical flow turbulators is carried out. According to the results of the analysis, it was determined that the investigated turbulators are more effective than classical ones, however, the pressure losses in the investigated turbulators are much higher. [ABSTRACT FROM AUTHOR]

To improve the performance of the compressed air energy storage (CAES) system, flow and heat transfer in different air storage tank (AST) configurations are investigated using numerical simulations after the numerical model has been experimentally validated. System performance for different AST placement methods is analyzed through numerical simulations integrated with the thermodynamic model of advanced adiabatic compressed air energy storage (AA-CAES). An in-depth study examines the impact of key system parameters on system performance with different AST configurations. Based on these analyses, the AA-CAES system with a constant volume of AST is optimized. The results indicate that horizontal placement of the AST improves heat transfer capability within the same working pressure range but results in slightly lower energy storage efficiency, achieving 64.61% compared to 65.50% for vertical placement. However, horizontal placement offers higher energy storage density, achieving 3.54 kW h/m3 under specific conditions, compared to 3.14 kW h/m3 for vertical placement. As the energy storage flow rate increases, exceeding the critical flow rate significantly improves heat transfer in vertically placed ASTs, thus narrowing the energy storage density gap between configurations. Increased turbine efficiency, additional external heat sources, and further utilization of compression heat provide more significant performance improvements for the AA-CAES with the AST placed horizontally compared to vertically. Compared to the AA-CAES with vertically placed ASTs, the configuration of the ASTs is optimized to enhance the electrical output of the AA-CAES by 76.4 MW h and reduce the input by 78.9 MW h at a storage flow rate of 0.5 kg/s. [ABSTRACT FROM AUTHOR]

The wind power curve serves as a critical metric for assessing wind turbine performance. Developing a model based on this curve and evaluating turbine efficiency within a defined health region, derived from the statically optimized power curve, holds significant value for wind farm operations. This paper proposes an optimized wind power curve segmentation modeling method based on an improved PCF algorithm to address the inconsistency between the function curve and the wind power curve, as well as the issues of prolonged curve modeling training time and susceptibility to local optima. A health region optimization method based on data increment inflection points is developed, which enables the delineation of the health performance evaluation region for wind turbines. Through the aforementioned optimization, the performance evaluation method for wind turbines is significantly improved. The effectiveness of the performance evaluation method is validated through experimental case studies, combining the wind power curve with the rotational speed stability, power characteristic consistency coefficient, and power generation efficiency indicators. The proposed modeling technique achieves a precision level of 0.998, confirming its applicability and effectiveness in practical engineering scenarios. [ABSTRACT FROM AUTHOR]

Wave energy converters (WECs) have significant potential to meet the increasing energy demands and using an oscillating water column (OWC) is one of the most reliable ways to implement them. The OWC has a simple structure and excellent durability. However, control of the power take-off (PTO) system is difficult due to variability in the input wave energy. In particular, the design and control of the PTO system are complex, as the average-to-peak ratio of the output generation is large. Owing to the nature of the OWC, if the energy above the rating cannot be controlled, the power generated is inevitably reduced due to the decrease in operating time. We propose a method to reduce the angular speed of the turbine by dividing the section according to the input energy and correspondingly changing the torque coefficient, thereby increasing the operating time of the OWC. The control methods for the PTO system of OWC are verified through a 30 kW full-scale experimental device to be installed in a real sea area. The full-scale experimental device consists of an inverter that simulates the mechanical torque of an OWC based on the aerodynamic simulation of an impulse turbine, an induction motor, a permanent magnet synchronous generator, an AC/DC converter, and a battery for the energy storage system. The performance of conventional control methods and the proposed method are compared based on the results of numerical simulations and experiments. We show that the fluctuation in the turbine angular velocity in the proposed method is significantly reduced compared with that in the conventional control methods under regular and irregular wave conditions. [ABSTRACT FROM AUTHOR]

Wind turbines are a solution for sustainable energy, significantly reducing carbon emissions and fostering a circular economy for more cost-effective and cleaner power generation, in line with worldwide environmental aspirations. In this context, this research aims to explore a novel two-stage, twisted-blade micro-Vertical-Axis Wind Turbine (μ -VAWT)alternative inspired by the Savonius Rotor (SR). This investigation utilizes the κ − ω SST turbulence model to explore the power coefficient ( C P ) and torque coefficient ( C T ), finding C P values ranging from 0.02 to 0.08 across the turbine by altering the free stream velocity (V). C T analysis further delves into four specific sections, highlighting areas of particular interest. These results are validated by examining velocity contours, pressure contours, and streamlines in four horizontal sections, demonstrating that the proposed turbine model exhibits minimal torque fluctuation. Moreover, the analysis of vertical wind streamlines illustrates very low interference with various wind turbine proposals, underscoring the turbine's efficiency and potential for integration into diverse wind energy projects. [ABSTRACT FROM AUTHOR]

This article focuses principally on the comparison baseline and the optimized flow efficiency of the final stage of an axial turbine operating on a gas–steam mixture by applying a hybrid Nelder–Mead and the particle swarm optimization method. Optimization algorithms are combined with CFD calculations to determine the flowpaths and thermodynamic parameters. The working fluid in this study is a mixture of steam and gas produced in a wet combustion chamber, therefore the new turbine type is currently undergoing theoretical research. The purpose of this work is to redesign and examine the last stage of the gas–steam turbine's flow characteristics. Among the optimized variables, there are parameters characterizing the shape of the endwall contours within the rotor domain. The values of the maximized objective function, which is the isentropic efficiency of the turbine stage, are found from the 3D RANS computation of the flowpath geometry changing during the improvement scheme. The optimization process allows the stage efficiency to be increased by almost 4 percentage points. To achieve high-quality results, a mesh of over 20 million elements is used, where the percentage error in efficiency between the previous and current mesh sizes drops below 0.05%. [ABSTRACT FROM AUTHOR]

The development of wind energy has been observed for many years. Both construction firms and the scientific world are analyzing new design solutions, atmospheric conditions and the technical performance achieved. The main goal of this research is to evaluate the requirements that have to be met to design wind power stations that would be an optimal fit for the climatic conditions in Poland. This study combines the results of empirical studies on wind velocity distributions with the physical fundamentals of wind power station design. This paper presents modelling of the relationships between wind velocity distributions observed in Poland and technical requirements for wind power stations design. The wind velocities distributions for various locations in Poland are determined and expressed in Weibull distribution parameters. Theoretical computations concerning the dependence of wind power stations as function of wind speed and air's physical properties are presented. Conclusions important for the design of power stations fitted to the atmospheric conditions in Poland are given. LabVIEW 2021 was used for computer modeling. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) exhibits intriguing thermo-physical properties such as higher heat capacity and conductivity, as well as a lower density than Ti6Al4V(ELI). These properties make SiC a good candidate for the reinforcement of Ti6Al4V(ELI) with respect to its use as a heat shield in aero turbines to increase their efficiency. The traditional materials used in aircraft structures were required to have a combination of good mechanical properties such as strength, stiffness, and hardness and low weight, as well as low thermo-physical properties such as coefficient of thermal expansion (CTE) and thermal conductivity. The alloy Ti6Al4V(ELI) has a density of 4.45 g/cm3, which is lower than that of structural steel (7.4 g/cm3) and higher than that of aluminium (2.5 g/cm3). Lower density benefits light weighting. Aluminium is the lightest of the traditional materials used but has relatively low strength. The CTE of SiC of 4.6 × 10−6/K is lower than that of Ti6Al4V(ELI) of 8.6 × 10−6/K, while the density of SiC of 3.21 g/cm3 is lower than that of Ti6Al4V(ELI) of 4.45 g/cm3. Therefore, from the theory of composites, SiC/Ti6Al4V(ELI) composites are expected to have lower densities and CTEs than those of Ti6Al4V(ELI), thus providing for lightweighting and less thermal related buckling or separation at their joints with carbon/epoxy resin panels. The specific strength, stiffness, and Knoop hardness of SiC of 75–490 kNm/kg, 132 MNm/kg, and 600–3800 GPa, respectively, are generally larger than those of Ti6Al4V(ELI) of 211 KNm/kg, 24 MNm/kg, and 880 GPa, respectively. Therefore, investigating reinforcement of Ti6Al4V(ELI) with SiC particles is worthwhile as it will lead to the formation of composites that are stronger, stiffer, harder, and lighter, with lower values of CTE. For additive manufacturing, this requires initial studies to optimise the process parameters of laser power and scanning speed for single tracks. To print single tracks in the present work, different laser powers ranging from 100 W to 350 W and scanning speeds ranging from 0.3 m/s to 2.7 m/s were used for different SiC volume fraction values of values. To print single layers, different values of hatch distance were used together with the best values of laser power and scanning speed determined elsewhere by the authors for different volume fractions of SiC. Through optical microscopy, the built tracks and their cross sections were examined. By using laser power and scanning speeds of 200 W and 1.2 m/s, and 150 W and 0.8 m/s, respectively, the best tracks at 5% and 10% volume fractions were obtained, whereas the best tracks at 25% volume fraction were achieved using a laser power of 200 W and a scanning speed of 0.5 m/s. Furthermore, the results showed that the maximum SiC volume percentage of 30% resulted in limited or no penetration. Therefore, it is concluded from the study that parts with improved mechanical properties can be produced at SiC volume fractions ranging from 5% to 25%, while parts produced at the high volume fraction of 30% would have unacceptable mechanical qualities for the final part. [ABSTRACT FROM AUTHOR]

Al-Khirat gas power plant in Iraq experiences significant reductions in power output and efficiency during the hot and dry summer season as an effect of a decrease in air mass flow rate resulting from rising ambient temperatures. To address this issue, upstream cooling systems are implemented and their performance is evaluated through energy and exergy analysis. This study tends to do a comparative study of a gas turbine performance with and without upstream cooling systems with power output, thermal efficiency, exergy efficiency, specific fuel feeding, consumed fuel mass flow rate, and exergy destruction rates. The findings show that upstream cooling systems (UPCS) can effectively mitigate the negative effects of high ambient temperatures on gas turbine performance, especially in Iraq's hot, dry summers. Our study found that higher air temperatures led to a significant drop in gas turbine efficiency, with a 35 K increase in inlet air temperature reducing power production by 27.4%. However, implementing UPCS increased thermal efficiency by 11.5% and exergy efficiency by 11.2%. [ABSTRACT FROM AUTHOR]

This study investigates the effects of low Reynolds number (Re) conditions on the cooling performance of fan-shaped film cooling holes in the gas turbine engines of high-altitude long-endurance Unmanned Aerial Vehicles (UAVs). The significance of film cooling technology becomes paramount due to the low Re operational environment of UAVs. A novel Very Large Eddy Simulation (VLES) method was employed to systematically analyze a range of mainstream Reynolds numbers (ReD) from 480 to 32 000 and blowing ratios (M) from 1.0 to 2.5 while keeping the density ratio (DR) constant at 1.75. Compared to other turbulence models, the VLES model showed the highest similarity in predicting thermal field distributions and the most accurate prediction of film cooling performance at low Re. The results reveal that at low ReD, significant flow concentration within the hole leads to reduced velocity uniformity at the outlet, resulting in poor film coverage downstream. Additionally, the coolant jet tends to detach from the wall, adversely affecting cooling performance. In contrast, higher ReD exhibited improved coolant jet adhesion to the wall and cooling efficiency, attributed to the reduced intensity of counter-rotating vortex pair and decreased hot gas entrainment, thereby enhancing cooling effectiveness. Notably, for the same ReD values, cases with M = 1.5 consistently showed better cooling effectiveness compared to other M conditions. This study provides new insight into the cooling performance of fan-shaped film cooling holes under low Reynolds number conditions, which is crucial for enhancing the cooling efficiency of gas turbines in high-altitude UAVs. [ABSTRACT FROM AUTHOR]

Working toward replacing conventional fossil fuels with alternative renewable energy, offshore renewable energy technologies give promising solutions, even though each of the types (wind, wave, tidal and thermal) is at a different stage of development and with its own unique challenges and opportunities. This paper is focused on sea wind wave energy harvesting through a hybrid system that combines both a water turbine with oscillating blades and "Wells"-type air turbine. A test bench was designed and tested at different flow rates to study the performance of the hybrid system and more precisely the "Wells"-type turbine. Experimental studies of the main parameters of a turbine were conducted, which demonstrated the efficiency of the turbine and its good practical application. The experimental results show good agreement with the preliminary performed numerical simulations, as well as with the published data. [ABSTRACT FROM AUTHOR]

Indonesia's vast maritime territory offers a unique opportunity for harnessing the potential Energy of seawater currents. This study explores the effectiveness of a combined Savonius and propeller-type turbine system. The Savonius turbine, known for its efficiency in capturing ocean currents due to its large sweep area, is combined with a propeller-type turbine to enhance rotational speed and power generation. A novel approach is employed to induce turbulence and optimize energy extraction, first channeling water through the propeller turbine and then into the Savonius turbine. A comprehensive investigation is conducted through simulations and experimental tests within a controlled tunnel environment. The study explores the performance of two-bladed and three-bladed Propeller-Savonius configurations at varying inlet water velocities (0.1, 0.3, 0.6 and 1.0 m/s). The simulation incorporates a turbulence model with 5% intensity and a hydraulic diameter of 0.216 m. Results indicate that the proposed configuration achieves a maximum power output of 2.0293 W with an impressive efficiency of 63.339% in simulation. Concurrently, experimental testing yields a peak efficiency of 61.335% and turbine power of 0.3951 W. The findings demonstrate the feasibility of the combined turbine system and highlight the importance of turbulence in optimizing energy extraction from seawater currents. This research contributes valuable insights into the design and performance of hybrid turbines for harnessing oceanic Energy, emphasizing the potential for sustainable power generation in maritime regions. The methodology and results presented herein offer a foundation for further exploration and refinement of seawater current energy conversion technologies. [ABSTRACT FROM AUTHOR]

When less water is available, hydropower turbines are less efficient, or have to stop altogether. This reality is often neglected in recent work on the planning and operations of hydropower systems, despite widespread expected increases in drought intensity, frequency and duration. This paper is the first to integrate variable‐efficiency turbines into a hydropower plant design framework that accounts for design optimization as well as deep uncertainty in climatic and socio‐economic variables. Specifically, this framework focuses on leveraging multi‐objective robust decision making for the financially robust design of run‐of‐river hydropower plants, whose output is highly sensitive to flow variability. Application to five plants in Türkiye challenges two key design assumptions, use of net present value as a design objective and use of identical turbines. Instead, maximizing the benefit‐cost ratio yields plants with better financial viability over a range of plausible futures. They tend to have smaller capacity, and feature a small turbine that is well‐adapted to low‐flow periods. Another key insight is that socio‐economic uncertainties have as much or even more impact on robustness than climate conditions. In fact, these uncertainties have the potential to make many small hydropower projects too risky to build. Our findings are of considerable practical relevance at a time where 140 GW of unexploited small hydropower potential could help power the energy transition. They also highlight the need for similar research in reservoir‐based plants, considering over 3,000 such plants planned or in construction worldwide. Key Points: Traditional approaches to hydropower planning need to be revisited to account for the impact of a variable climate on turbine efficiencyMaximizing the benefit cost ratio rather than the net present value promotes smaller designs, better adapted to a drought‐prone worldSocio‐economic and climatic factors are both crucial to design financial robustness [ABSTRACT FROM AUTHOR]

AbstractA new in-pipe hydropower prototype having a novel internal flow separator, denominated as P20, was developed and tested to achieve Technology Readiness Level (TRL) 6. The P20 separates water into main channel where the water flow is uninterrupted and two power generation (PG) purpose channels with nozzle and turbine system, respectively, at each side. The P20 also has valves for turbines maintenance and service work purposes at the PG channels’ inlets and outlets. From the performance test, 28.8% of pressure loss is created at the maximum flow condition (0.076 m3s−1 flow rate that produced 1.25 bar of stagnation pressure). At this condition, each turbine produced mechanical power of 55 W with 35.9% of turbine efficiency. The highest turbine efficiency recorded in this study was about 42% obtained at a flow rate 59% of the maximum condition, where less water filled the turbine casing as compared to the maximum flow condition. PG channel size also affects the turbine efficiency. Overall, the P20 has been functioning according to the design that allows the majority of water to flow uninterruptedly while concurrently generating in-pipe hydropower.

Tubular axial turbines (TATs) play a crucial role in mini and micro hydropower setups that require simplified yet reliable solutions. In very low head scenarios, single regulation in TATs is common, due to economic impracticality of the sophisticated mechanisms involved in the conjugate distributor–rotor regulation typical of the Kaplan turbines. Distributor or rotor single regulation strategies offer operation flexibility, each with distinct advantages and disadvantages. Stator regulation is simpler, while rotor regulation is more complex but offers potential efficiency gains. The present paper analyzes energy losses associated with these regulation strategies using two approaches: 1D mean line turbomachinery equations and 3D Computational Fluid Dynamics (CFD). The 1D mean line approach is used for understanding the conceptual fluid dynamic aspects involved in the two different regulation approaches, thereby identifying the loss-generation mechanisms in off-design operation. Fully 3D CFD simulations allow for quantifying and deeply explaining the differences in the hydraulic efficiencies of the two regulation strategies. Attention is focused on the two main loss contributions: residual tangential kinetic energy at the rotor outlet and entropy generation. Rotor regulation, even if more complex, provides better results than distributor regulation in terms of both effectiveness (larger flow rate sensitivity to stagger angle variation) and turbine operating efficiency (lower off-design losses). [ABSTRACT FROM AUTHOR]

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